Recent advances in wireless communication technologies have led to the popularization of mobile devices. To keep pace with the advanced wireless technologies, there is a strong tendency to essentially use secondary batteries as power sources for devices. On the other hand, electric automobiles and hybrid automobiles are currently being developed for the purpose of preventing environmental pollution. These vehicles also use secondary batteries as power sources.
In many other industrial fields, there has been a dramatic increase in the frequent use of secondary batteries. The power output, capacity and structure of secondary batteries become more diverse depending on the characteristics required in applications they are used.
Generally, a secondary battery includes an electrode assembly having a configuration in which a separator is interposed between a cathode and an anode, each of which is produced by applying an electrode active material to the surface of a planar current collector. The electrode assembly is usually accommodated in a cylindrical or prismatic metal can or a pouch-type case made of an aluminum laminate sheet, together with a liquid or solid electrolyte. Alternatively, the electrode assembly may have a jelly-roll configuration in which a sheet-like cathode/separator/anode structure is wound, or a structure in which a plurality of thin plate-like unit electrodes are laminated sequentially. This configuration or structure is advantageous in enhancing the capacity of the secondary battery. In any case, all electrodes (i.e. the cathode and the anode) of the electrode assembly structures are essentially planar in shape.
Such conventional planar electrode structures have the advantage of high degree of integration upon winding or lamination, but have a limitation in that they are difficult to structurally modify according to the needs of industrial fields. The planar electrode structures are susceptible to changes in the volume of the electrodes during charge and discharge. Other problems of the planar electrode structures are that gases produced from the cells do not easily escape outside and there may be a large potential difference between the electrodes.
Particularly, diverse kinds of devices using secondary batteries have emerged in the market in response to various needs of consumers, and their designs have gained importance. Despite this trend, even specially designed devices necessitate additional areas or spaces where secondary batteries having traditional structures and/or shapes (cylindrical, prismatic or pouch type) can be mounted. This necessity is considered a major obstacle in extending wireless technologies or overcoming the limitations of design. For example, to mount a secondary battery in a narrow and long space of a newly developed device, it is substantially impossible or very inefficient to structurally modify a secondary battery including an electrode assembly based on planar electrodes that are currently in use. That is, conventional cylindrical, coin-type and prismatic batteries are difficult to structurally modify (e.g., distort or bend) in an arbitrary manner depending on where they are used, due to their predetermined shapes. In an attempt to solve these problems, an electrode assembly having a new structure and a secondary battery including the same are disclosed in Korean Patent No. 10-0804411, which was filed by the present applicant on Jan. 17, 2006 and was patented on Feb. 12, 2008, the contents of which in its entirety are herein incorporated by reference.
However, heat is produced from the secondary battery (hereinafter, also referred to as a “cable-type secondary battery”) during charge and discharge, leading to a temperature rise of the battery. As a result, the battery suffers from performance deterioration and a user may feel discomfort or even may get burned upon contact with the battery.